Fluid conduit and method for making same



Nov. 29, 1966 R. T. HUCKS, JR 3,288,171

FLUID CONDUI'I AND METHOD FOR MAKING SAME l i r Original Filed Sept. 29.1961 INVENTOR. v RoBERr T- Huc s JR A TTORMEV United States Patent Wm3,288,171 FLUID CONDUIT AND METHOD FOR MAKING SAME Robert T. Hucks, Jr.,Somerville, NJ., assignor to Johns- Manville Corporation, New York,N.Y., a corporation of New York Original application. Sept. 29,. 11961,Set. No. 141,849, now Patent No. 3,219,472, dated Nov. 23, 1965'.Divided and this application Feb. 10, 1965, Ser. No. 431,635 4 Claims.(Cl. 138-145) This application is a division of application Serial No.141,849, filed September 29, 1961, now US. Patent No. 3,219,472, whichapplication is a continuation-in-part of application Serial No. 756,638,filed August 22, 1958 and now abandoned.

The present invention relates to fluid conduit, such as pipe, providedwith a coating on its interior surface, and to a method for producingsuch conduit. The invention is concerned with porous pipe such asfibro-cement pipe and with coatings which, although applied in a hotliquid form, may be cured to a solid fluid-impervious state. The

- method of the invention, while useful in providing substantially anytype of porous pipe with any type of coating which is applied in hotliquid form and is then cured to a solid fluid-impervious state, isparticularly useful in producing fluid conduit comprising fibro-cementpipe having on its interior surface a cast coating including a fillermaterial and a particular type of thermosetting resin.

It has long been recognized as desirable, in the adaptation of porouspipe for use as fluid conduit, to provide the pipe with an interiorcoating which will be smooth, hard, fluid-impervious andchemical-resistant and which will be firmly bonded to the pipe, butgreat difiiculty has been experienced in actually attaining the desireddegree of fluid-imperviousness in the coating and the desired firmnessof bond of the coating to the pipe by any method which is economicallyfeasible when the pipe is composed of fiber and cement. Perhaps the mostconvenient general method of applying a coating to the interior of afibro-cement pipe is by what will here be termed as casting, i.e., bydistributing the coating in liquid form onto the interior surface of thepipe and spinning the pipe about its axis to cast the liquidcentrifugally into a layer of substantially uniform thickness withportions thereof penetrating the pores of the pipe. Casting methodswhich have previously been used for coating cementitious pipe, however,either are economically unsuited for coating fibro-cement pipe orproduce coatings which either are not completely bonded to the pipe orinclude such a large number of minute holes (termed pin holes) as to besomewhat pervious to fluids.

One prior casting method employed in coating cementitious pipe isdisclosed in US. Patent No. 2,962,052 and involves casting on theinterior of a concrete pipe a liquid coating composition comprising apolyester resin and a filler, both the coating composition and the pipebeing at ambient temperatures and the coating being air cured to a solidstate. This method has been found unsatisfactory for coatingfibre-cement pipe because with both the coating composition and pipe atambient temperatures there not only is insufficient penetration of thecoating into the pores of the pipe to bond the coating firmly to thepipe but also there is such a relatively long period required for aircure that the process is economically unfeasible. In a second priorcasting method, the coating composition is relatively hot while the pipeis either at ambient temperatures or is heated at its exterior surface.This second method, at least when applied to fibre-cement pipe, has beenfound to result in an excessive number of pin holes and/or blisters sothat it has been found difiicult or impossible to secure an interiorcoating on the 3,288,171 Patented Nov. 29, 1966 pipe which is smooth,fluid-impervious and firmly bonded to the pipe.

One object of the present invention is to provide a fluid conduitcomprising a smooth, hard, blister-free, fluid imperviouschemical-resistant coating firmly bonded to the interior surface of afibre-cement pipe.

Another object of the present invention is to provide a method ofcoating the interior surface of a fibre-cement pipe which method iseconomically feasible and results in a coating which is firmly bondedand free of pin holes and blisters.

In brief, the above objects are attained in the present invention bycasting a heated liquid coating on the interior surface of afibro-cement pipe which has been heated prior to casting toapproximately the same temperature as the heated coating but which pipe,during casting, is in a state of cooling from the outside so that itsexterior surface is significantly lower in temperature than the interiorsurface. This method of coating, while useful with many coatingmaterials to prevent blisters and pin holes and to secure a firmlybonded smooth coating, is particularly useful with heat reactablecoating materials comprising catalyzed thermosetting resins such asepoxy, polyester and polyurethane resins which produce 'hard,chemical-resistant coatings. It is believed that the method of thepresent invention attains the desired result by carrying heat away fromthe interior surface of the pipe through the pipe wall during casting,thereby eliminating the formation and/or further expansion of gases orvapor in the pores of the pipe at the interior surface after the castingprocess has begun, such formation and/or expansion possibly having beenthe cause of the blisters and pin holes which resulted from priormethods of applying 'hot liquid coating materials to the interiorsurface of the pipe. The method is therefore particularly useful wherethere is an exothermic reaction in the coating during casting.

The invention will be more fully understood and further objects andadvantages thereof will become apparent when-reference is made to thefollowing detailed description of a preferred embodiment of theinvention and the accompanying drawings in which:

FIG. 1 is an end elevation of apparatus suitable for carrying out themethod of the invention; and

FIG. 2 is a pictorial representation of a coated pipe.

Referring to the drawing there is disclosed in FIG. 1 apparatus adaptedto perform the method of the instant invention so as to provide a fluidconduit comprising a porous fibro-cement pipe having on the interiorsurface thereof a cast, hardened, smooth, blister-free andfluidimpervious coating. A fibro-cement pipe 1 is supported on rollers 2and 3 for rotation thereon. The roller 2 is supported in the positionshown for rotation in suitably mounted conventional journal boxes (notshown) and is rotated by a conventional driving belt 4 which isconnected to a suitable source of power 5, such as a variable speedmotor. The arrangement is such that the speed of rotation of the roller2 can be varied selectively and controlled as desired. The roller 3 isjournalled for rotation in suitably supported conventional journal boxes(not shown) which are mounted for adjustment in a horizontal plane. Theadjustment of the roller 3 allows the apparatus to accommodate differentsizes of fibro-cement pipe for rotation on the rollers 2 and 3. Asuitable mechanism 6 applies the heated liquid resin coat-ing materialto the inner surface of the fibro-cement pipe in a conventional manner.

In accordance with the method of the instant invention, a fibro-cementpipe is heated to a predetermined temperature approximating that of theliquid resin coating material and then placed on the rollers 2 and 3.The

fibre-cement pipe is rotated at a predetermined speed by the roller 2driven by the power source 5. During rotation of the fibro-cement pipeand while it is in a state of cooling primarily at its exterior surface,a heated liquid resin coating material is applied to the inner surfaceof the pipe through the mechanism 6. The heated liquid resin coatingmaterial is applied in sufficient quantity that a coating of desiredthickness will be formed on the inner surface of the fibro-cement.pipe.The rotation of the fibro-cement pipe is continued until the heatedliquid resin coating material has solidified or set up to the point ofresisting flow or slumping. It is necessary that the speed of rotationof the fibre-cement pipe be sufliciently high that any ripples in theresin coating will be removed and that the coating material will be heldon the pipe wall. The peripheral speed of the pipe preferably is from100 to 360 feet per minute. After the coating material has solidified orset up to the point of resisting flow or slumping, the pipe is removedfrom the rotating means and the coating is allowed to continue curing ina conventional manner. The resulting product, as shown in FIG. 2,comprises a fibro-cement pipe having on the interior surface thereof acast, hardened, smooth, blister-free, fluidimpervious coating, so thatthe fibre-cement pipe may be used in situations or services requiringfluid imperviousness and a smooth surface over which the flow of thefluid to be'transmitted through the pipe is directed. The fibrocementpipe may also be used in situations or services requiring high chemicalresistance to fluids to be carried by the pipe by selection of coatingmaterial which will. exhibit that property after the completion of theprocess in the resulting product.

In practicing the method of the instant invention, there are certainprocedures that should be followed. The fibro-cement pipe mass ispreheated to a temperature which is approximately the same as theapplication temperature of the resin coating material. The applicationtemperature level of the liquid resin coating material, and in turn ofthe pipe mass, is dictated primarily by the curing and handleability orapplication characteristics of the particular resin coating material.Temperatures for curing and application conditions, e.g., providingmanageable viscosities, for the foregoing identified resinous materialssuitably filled to control subsequent shrinkage, comprise a range offrom about 125 up to about 375 F. The heated, liquid coating material isdistributed over the inner surface of the heated pipe by any suitablemeans such as by spraying, etc. During the application of the hot liquidcoating material, the pipe is in rotation, so as to cast the hot liquidcoating material into a continuous layer of substantially uniformthickness coterminous with the interior surface of the pipe. Thecentrifugal forces established by the rotation of the pipe and theviscosity of'the hot liquid coating material cooperate to effectsubstantial penetration of the hot liquid coating material into thepores adjacent the interior surface of the pipe to form an integral bondtherewith. The rotation of the coated pipe is continued until the liquidcoating material solidifies or sets up to the point of resisting flow orslumpmg.

During the application of the hot liquid coating material to theinterior surface of the rotating fibro-cement pipe and during curing ofthe coating material on the interior surface of the rotating pipe untilthe coating material solidifies or sets up to the point of resistingflow or slumping, certain temperature conditions should prevail so thata blister-free and fluid-impervious coating is provided. At the time ofapplication the temperature of the liquid coating material should beapproximately the same as the temperature of the inner surface of thepipe and the inner surface of the pipe should be at a higher temperaturethan the exterior surface so that a generally descending temperaturegradient exists between the two surfaces. The required temperaturegradient seems to exist naturally, for example, when a heated standard6-inch asbestos-cement pipe is rotated at about 120 rpm. For large sizeasbestos-cement pipe, such as 36-inch pipe, it may be necessary to coolthe exterior surface in order to secure the desired generally descendingtemperature gradient. If the hot liquid coating material is eitherappreciably hotter or cooler than the interior surface of the pipe, orif the generally descending temperature gradient is not maintained, blowholes result to mar the surface and usefulness of the resin coating forthe fibre-cement pipe. However, small deviations in the temperature ofthe coating materials are permissible since the relative wall thicknessof the coating material is small as compared to that of the pipe and thetemperature of the coating material will rapidly conform to thetemperature of the interior surface of the pipe.

Under the foregoing operating conditions, the fibrocement pipe is in astate of cooling during the coating operation so that the temperature ofthe inner surface of the fibre-cement pipe is falling and thus causing acontraction of gases or vapor in the pores of the pipe. The temperatureof the coating material must be such that this condition is notdestroyed and a slightvacuum prevails in the walls of the fibro-cementpipe as the coating is applied. This vacuum cooperates with thecentrifugal forces due to the rotation of the fibre-cement pipe and theviscosity of the hot liquid coating material to effect maximumpenetration of the hot liquid coating material into the pores of thefibre-cement pipe adjacent the interior surface thereof to form anintegral association and intimate bonding of the resin coating materialand the fibrocement pipe.

If the asbestos-cement pipe is heated during the coating operation orthe curing of the liquid resin coating material, blow holes are producedin the coating. When heat is applied to the exterior of the fibre-cementpipe during the coating operation, the desired temperature gradient isreversed with the greater temperatures occurring at the outer surface ofthe fibro-cement pipe. This forces the gases and/ or vapor toward thecoating to form blow holes therein. Thus, as indicated in theexplanations above, it is essential to maintain a temperature gradientin the fibre-cement pipe wherein the greater temperature is at the innersurface of the fibro-cement pipe during the application and curing ofthe coating material.

Suitable coating materials for use in accordance with the instantinvention comprise liquid resin compositions (as opposed to solventdispersed solid resin sytems) which are curable to an infusible,durable, chemicalresistant resin. Preferred materials consist of thoseresin materials which exhibit an aflinity for and/or tolerateasbestos-hydraulic cement compositions and which are easily convertedupon application from a liquid to solid state and cured by appropriatecatalysts and elevated temperatures. Effective catalyst and/or reactionaccelerating heat conditions may be in accordance with those provided bythe resin vendor or as prescribed by the knowledge of the art. Whenemployed in connection with epoxy and the like resin the term catalystis to be understood as embracing the conventional hardening agentsnormally utilized therewith. Examples of the preferred class of coatingmaterials include catalyzed thermosetting epoxy, polyester, andpolyurethane resins. These resins are not detrimentally affected by thealkali conditions normally found in calcareous cementitious materialsand provide liquid coating materials of handleable viscosities atrelatively low temperature even when filled, and may be economicallyapplied and cured under industrially feasible conditions by heatreacting at temperatures between about F. and about 350 F., and, whencured, provide particularly durable coatings resistant to the acidconditions frequently found in sewerage and industrial applications.Liquid coatings in thicknesses of from 8-60 mils, prepared and/orapplied to the pipe in accordance with the foregoing prescribedconditions, may be heat and catalyst reacted in situ to a degree ofsolidification effectively resisting flow o r slumping within about 3 to6 minutes with the cure being completed in an overall period of about 5to 20 minutes from application at the relatively low temperature ofapproximately 125- 350 F.

To offset any shrinkage normally encountered during the curing oft-hermosetting resins, and, in turn, depending upon the circumferentialarea of the coating, i.e., diameter of the pipe coated, the resin shouldbe filled with finely divided, chemically resistant or substantiallyinert particulate material such as sand, ground glass and the like inamounts of up to approximately 60% by weight of the coating composition.Fillers in proportion of about 20-60% by weight of the composition havebeen found effective in controlling the shrinkage encountered withtypical thermosetting resin coatings in average size fibro-cement pipe.

The examples below illustrate the improved method of applying thechemical-resistant, fluid-impervious coatings to the interior surface offibro-cement pipe and the coated products thereof. It is to beunderstood that the compositions of the particular resin coatings andthe relative proportions of the constituents thereof set forth in theseexamples are all exemplary and are not to be construed as limiting thenovel method or means of this invention to any specific compositionsrecited in these examples.

In each of the following examples, the fibre-cement pipes employed had a6-inch inside diameter with a wall thickness of %-iuch and the rate ofrotation of the pipe throughout each procedure was approximately 120revolutions per minute. Also, percentages and/or parts ratios given inthese examples are all based upon weight. The coating produced in eachof the examples was well bonded, smooth and ripple free throughout theinterior surface of the pipe.

Example 1 A liquid coating material, comprising 60% by weight ofbisphenol A-epichlorohydrin resin (Epon 828, Shell Chemical Corporation)and 40% by weight of a finely divided silica, is combined with asilicone resin flow control agent (SR-82, General Electric Co.) in anamount by weight of 1 part of the silicone resin flow control agent per100 parts of the epoxy resin and with a triethylenetetramine curingagent in an amount by weight of 12 parts of the triethylenetetraminecuring agent per 100 parts of the epoxy resin at a temperature of 230F., was spray-applied over the interior surface of asbestos-cement pipesections previously heated to a temperature of 220 F. The amount appliedwas sufficient to provide a substantially uniform coating of about 20mils in thickness. Rotation of each pipe was continued for a period ofapproximately 6 minutes from time of application whereupon the resincoating had solidified to the point of resisting flow or slumping andthe cure of the hot resin coating was complete within about minutes fromthe time of application.

Examples 2 and 3 A liquid epoxy based resin coating formulation of 40%by weight of bisphenol A-epichlorohydrin resin and 60% by weight offinely divided silica filter is combined with a silicone resin flowcontrol agent (SR-82, General Electric Co.) in an amount by weight of 1part of the silicone resin flow control agent per 100 parts of the epoxyresin and with a triethylenetetramine curing agent in an amount byweight of 12 parts of the triethylenetetramine curing agent per 100parts of the epoxy resin maintained at a temperature of 240 F. wasuniformly sprayed throughout the interior of rotating sections offibro-cement pipe heated to 240 F. in amounts to provide coating liningswithin sections of pipe of either 20 mils or 40 mils in thickness. Inthe 20-mil thick coated pipe sections, the catalyzed heat reaction hadproceeded to the point of permitting termination of the rotation atapproximately 4 minutes following application with a complete cure beingeffected within about 8 minutes from application, and the reaction inthe 40-mil thick coated pipe products proceeded sufficiently rapidly topermit termination of rotation within about 3 minutes followingapplication with completion of the cure about 6 minutes afterapplication.

Example 4 A liquid coating formulation of 60% by weight of isophthalicpolyester (Aropol Q 6015, Archer, Daniels, Midland Company) and 40% offinely divided silica filler mixed with methylethylketone peroxidecatalyst in proportions of 1 part per parts of the polyester resin wasapplied, while at a temperature of F., to a thickness of 20 milsthroughout the interior of rotating sections of asbestos-cement pipeheated to 125 F. The polyester base coatings advanced to a state of curepermitting termination of rotation of each pipe section at approximately5 minutes after application, and cure thereof was completed in 15minutes from application.

Example 5 A liquid elastomer, comprising a polyether based urethaneelastomer (Adiprene L167, Du Pont( in amount of 83.3% by weight and4,4'-methylene-bis (Z-chloroaniline) (MOCA, Du Pont) in an amount of16.7% at 220 F. was applied as a 20-mil thick coating to rotatingfibrocement pipe sections also heated to 220 F., permitting terminationof rotation at approximately 3 minutes after application withdeformation, and the cure thereof was complete at about 5 minutes fromapplication.

Example 6 A liquid epoxy coating composition at a temperature of 240 F.and composed of 60% by weight of bisphenol A-epichlorohydrin with 40% byweight of powdered silica filler combined with a triethylenetetraminecuring agent in a ratio of 12 parts per 100 parts of the epoxy resin wasdistributed over the inner surface of asbestos-cement pipe to athickness of 40 mils. The temperature of the liquid coating compositionat application was 240 F. whereas the temperature of the rotating pipewas 250 F The catalyst-activated and heat-accelerated cure progressed tothe point of permitting termination of rotation of the pipe withinapproximately 5 minutes and the pipe was then post cured in an oven for2 hours at 250 F.

As shown by the above examples a difference of 10 F. between thetemperature of the coating material at the time of application and thetemperature of the interior surface of the pipe can readily betolerated. It is believed that satisfactory results may be obtained, andthat these two temperatures may be considered to be approximately thesame, or not appreciably different, when the actual difference is ashigh as about 20 F., but the greater this temperature difference thegreater this risk that pin holes and blisters will develop, and it ispreferable to maintain this difference as low as possible.

When applying a hot liquid resin coating material to a relativelylarge-diameter and thick-walled fibre-cement pipe, such as an 18-inchClass 200 asbestos-cement pipe having a wall thickness of approximately2.17 inches, in accordance with the method of the instant invention, itis sometimes necessary to apply distinct and additional cooling means tothe exterior surface of the fibro-cement pipe so thatthe propertemperature gradient, as described above, exists in the pipe. One suchcooling means comprises a water spray positioned to distribute coolingwater to the exterior surface of the rotating pipe during the coatingand initial curing operation. Any other desired type of cooling meansmay be applied to the exterior surface of the pipe to insure that thetemperature gradient, as explained above, exists in the pipe and thatthe temperature adjacent the interior surface of the pipe is notsubstantially increased after the application of the hot liquid resincoating material.

In those instances wherein the method of the instant invention ispractice-d at temperatures exceeding 212 F it is desirable to removemoisture from the fibre-cement pipe prior to the coating operation. Whencoating 6-inch Class 150 asbestos-cement pipe, the uncoated pipe isplaced in an oven and maintained at 240 F. for sixteen hours. If theexcessive moisture is not removed from the pipe, the continuinggeneration of steam within the walls of the pipe tends to cause theformation of blowholes or other imperfections in the coating wherebythere does not result the formation of a smooth, continuous, uniform,blister-free and fluid-impervious coating on the interior surface of thepipe. In those instances where the method of the instant invention ispracticed at temperatures less than 212 F., it is not necessary toremove the moisture from the pipe.

As stated in the foregoing description, the instant invention is usefulin the coating of porous fluid conduit such as fi'bro-ceme'nt pipe, andespecially asbestos-cement pipe, which is well known and extensivelyused commercially. Such asbestos-cement pipe typically comprisesasbestos fibers and a binder comprising hydrated, hardened hydraulicsetting (Portland) cement. The invention is particularly applicable tosuch asbestos-cement fluid conduit in its cured state, in which thecement is hardened or set to a shape-retaining condition, prior to thecoating operations, but it is recognized that green or uncuredasbestos-cement fluid conduit could be coated by applying the conceptsof the invention.

While the invention has been described in rather full detail, it will'be understood that these details need not be strictly adhered to andthat various changes and modifications may suggest themselves to oneskilled in the art, all falling within the scope of the invention asdefined by the subjoined claims.

What I claim is:

1. A fluid conduit comprising:

(a) a porous fibro-cement pipe having on the interior surface thereof acast, hardened, smooth, blisterfree, and fluid-impervious coating,

(b) said coating penetrating pores of said interior surface to form anintegral bond therewith,

(c) said coating comprising a heat-reacted, catalyzed,

liquid, thermosetting resin, and

(d) said coating being between about 8 and about 60 mils in thickness.

2. The coated fluid conduit of claim 1 wherein the coating comprisescatalyzed thermosetting resin selected from the group consisting ofepoxy, polyester and ure- 10 thane resin.

3. A fluid conduit comprising:

(a) a porous fibre-cement pipe having on the interior surface thereof acast, hardened, smooth, blister-free, and fluid impervious coating,

(b) said coating penetrating pores of said interior surface to form anintegral bond therewith,

(c) said coating comprising a heat-reacted, catalyzed,

liquid, thermosetting resin and filler,

(-d) said filler being between about to about 50,

20 percent by weight of the total composition of said resin and saidfiller, and

(e) said coating being between about 8 and about 60 mils in thickness.

4. The coated fluid conduit of claim 3 wherein the coating comprises anepoxy resin.

References Cited by the Examiner UNITED STATES PATENTS 1,618,540 2/1927Ligonnet 117 9sx 2,109,644 3/1938 Klingensmith 117-101 x 2,824,0782/1958 Mellick 117-161 x 2,962,052 11/1960 Sergovic 138145 FOREIGNPATENTS 521,902 6/1940 Great Britain.

LAVERNE D. GEGIER, Primary Examiner.

C. HOUCK, Assistant Examiner.

1. A FLUID CONDUIT COMPRISING: (A) A POROUS FIBRO-CEMENT PIPE HAVING ONTHE INTERIOR SURFACE THEREOF A CAST, HARDENED, SMOOTH, BLISTERFREE, ANDFLUID-IMPERVIOUS COATING, (B) SAID COATING PENETRATING PORES OF SAIDINTERIOR SURFACE TO FORM AN INTEGRAL BOND THEREWITH, (C) SAID COATINGCOMPRISING A HEAT-REACTED, CATALYZED, LIQUID, THERMOSETTING RESIN, AND(D) SAID COATING BEING BETWEEN ABOUT 8 AND ABOUT 60 MILS IN THICKNESS.